Ok, front brake and no rag joint. That's good. I would still replace the tensioner with an engine mounted one. Even if the bracket cannot turn on the frame, it can still bend, or that white plastic roller can break, allowing the loose chain to come off the sprocket and lock up the rear wheel. On a single speed it might be possible to remove some links from the chain and adjust it by sliding the axle in the frame. I know that could throw the pedal chain out of adjustment, but you should be able to get it close with a half link. I would much rather the pedal chain be a little off than the motor chain. My Trek 800 used to be an 18 speed, and I converted it to a single speed, by removing the derailleurs and all but the smallest front sprocket. I put the chain on the largest sprocket on the rear wheel, so I would have a really low gear. I couldn't get the chain adjusted perfectly because of the vertical rear dropouts, so I rode it with the chain a little bit loose for awhile, the finally got a new chain and reinstalled the rear derailleur just to act as a tensioner. No motor chain, it's friction drive.